Technical Abstract:
Measuring oxygen consumption on fish eggs or fry with polarigraphic or galvanic oxygen sensors can be problematic. The water current necessary for accurate dissolved oxygen (DO) reading can damage the fragile organisms. We developed a micro-respirometer chamber to measure oxygen consumption on channel catfish Ictalurus punctatus eggs using a luminescent dissolved oxygen sensor and meter.
The respirometer was made with a 266 ml clear wide mouth glass jar. A 2.54 cm dia. hole was drilled in the cap through which a 7.1 cm long X 1.90 cm I.D. schedule 80 threaded PVC pipe was inserted. The pipe was secured with two aluminum conduit washers and sealed with clear silicone caulk. An O-ring was glued to the inside end of the pipe with super glue. The O-ring provided a seal around the oxygen probe which was inserted through the pipe. The pipe also served to contain overflow created by insertion of the probe into the chamber. A 0.24 cm hole was drilled through the lid near the edge. A 2.54 cm length of capillary tube was inserted in the hole and glued flush with the inside surface with super glue. This tube was used to bleed off any air trapped in the jar. A short platform was made to suspend the eggs above the magnetic spin bar used to circulate water within the chamber. When the probe was inserted through the pipe, it extended through the O-ring and into the chamber approximately 2.2 cm, exposing the probe temperature sensor to the water.
Spawn samples were drained, weighed and placed in the chamber, and the probe inserted. The chamber was submerged in a water bath on a magnetic stir plate and hatchery water circulated through the bath. The spin bar was rotated at a speed that agitated the spawn similarly to that seen in commercial hatcheries. DO and temperature measurements were recorded at one- to five-minute intervals. Oxygen consumption was measured on several spawns over a five-day incubation period. Measurements on sac fry and swim-up fry were made using a BOD bottle and a probe-tip micro spin bar. Both systems worked well.